This invention relates to a current to pressure transducer, and more particularly to an electro-pneumatic transducer which converts a current input to a proportional pneumatic output.
Current designs, such as known from U.S. Pat. No. 4,481,967, use a piezoelectric beam driven with a single polarity voltage or a magnetically susceptible element suspended in a magnetic field. The devices which have an element suspended in a magnetic field use a stationary coil to create a net force on the element, moving it toward a nozzle to create a back pressure. Devices which have a piezoelectric beam use a single polarity voltage to drive the beam. A piezoelectric beams' position will creep over time with the applied voltage. The direction of the creep is toward the neutral position. In the case of a single polarity voltage, the beam will eventually creep until the drive voltage can no longer control the beam to achieve the specified output range. Another problem with the piezoelectric beam is the creep due to temperature fluctuations. The polarization of the beam will cause break down when a specified voltage, per mil of piezoelectric beam thickness, is exceeded. The single polarity drive will allow a limited amount of excess voltage to compensate for temperature creep of the piezoelectric beam.
Accordingly, the problems of the prior art are overcome by the invention which incorporates a dual polarity drive voltage.